import java.util.*;


public class Lista<Tipo> {
	
	private ArrayList<Tipo> info;
	private int head;
	
	public Lista()
	{
		
		info=new ArrayList<Tipo>();
		head=-1;
		
	}
	
	public void addFirst(Tipo elemento)
	{
		if(head==-1)
			head=info.size()-1;
		
		info.add(elemento);
	}
	
	public Tipo removeFirst()
	{
		int tam;
		tam=head;
		
		if(head==-1)
			return null;
		else
		{
			if(info.size()>(head+1))
				head=head+1;
			return info.get(tam);
		
		}
	}
	
	public boolean vacio()
	{
		if (head==-1)
			return true;
		else
			return false;
	}
	

}
